Observations using a two-wavelength polarization lidar (1,064 nm and 532 nm, dual polarization at 532 nm) were performed at the same time with a 95-GHz cloud profiling radar on the Mirai MR01-K02 ACE-Asia cruise. The lidar observed plumes of Asian dust and anthropogenic aerosols in the Northwest Pacific. The data were analyzed using an inversion method and a new forward algorithm for two wavelength lidars based on assumptions on the characteristics of aerosols. The results revealed layered structure of sea salt, sulfate and Asian dust plumes. Microphysical parameters of clouds were derived with a radar/lidar combined data analysis algorithm. Experiments on bistatic lidar measurements of water cloud particle size were also performed on the cruise.
Assessment of spatial distribution and variation of optical properties and chemical species in atmospheric aerosols is essential to estimate the direct climate forcing. In the western North Pacific, where pollutants are transported from the East Asia, there are few aerosol measurements available to estimate the climate forcing. In this study the aerosol optical and chemical properties were measured during June-July 2000 (MR00-K04 cruise) and May 2001 (MR01-K02 cruise) in the western North Pacific on board the research vessel Mirai during the ACE-Asia campaign. During MR00-K04 cruise, in the southern area of 30°N, it was found that the area was under marine background condition. The single scattering albedo (ω) ranged from 0.95 to 0.99. On the other hand, during MR01-K02 cruise, it was found that anthropogenic aerosols and soil particles originating from the Asian Continent were transported. Then, the ω ranged from 0.82 to 0.95 were measured, which were absorptive aerosols.
In order to study physical properties of marine aerosols, sampling and counting of aerosols between the surface and lower free troposphere were performed on board R/V Mirai during the MR00-K04 and MR01-K02 cruises. Two Kosa events were observed during the MR01-K02 cruise and an intensive observation was performed with the assistance of CFORS prediction. Continuous measurements of number size distribution between 4.4 and 5,000 nm in diameter in the surface air were carried out. The lifetime of aerosols which was estimated by the data of the size distribution and four tracers (Rn, ThB, CO, C2Cl4) was dependent on the size. The refractive index of aerosols was estimated by comparing the backward scattering coefficients obtained with kytoon and lidar. Furthermore, individual particles were analyzed with TEM/EDX and the degrees of modification and internal mixing of sea salt particles with dust were discussed.
Measurements of particle number density and particulate carbonaceous substances were conducted during the pre ACE-Asia cruise from June 13 to July 5, 2000. This was the preliminary cruise for the Japanese ACE-Asia cruise, covering the western North Pacific region including regions affected by the westerlies, tropical and subtropical regions. Air quality was clearly divided by the Bai-u front (a seasonal frontal system) , with high concentrations of anthropogenic aerosols north of the frontal system and low concentrations to the south. The position of the front and the development of Pacific anticyclone are the primary factors that influence outbreaks of polluted air masses over the western North Pacific in early summer. Relatively high concentrations of organic carbon were also detected over the tropical region, suggesting emission of precursor gases for particulate organic carbon from the ocean. The size-distribution of particle number density suggests that new particle production is activated over the tropical ocean.
In order to study the chemical composition of marine aerosol and an impact caused by the primary production in spring season, aerosol sampling and measurement of dimethylsulfide (DMS) concentration were carried out on board of R/V Mirai during MR01-K02 cruise from May 14 to 28 2001. Based on the relationship between in-situ seawater DMS concentration and chlorophyll-a (CHL-a) estimated from satellite, amount of DMS emitted from the sea surface is estimated along the way of air parcel. MSA concentration observed on May 25 and 27 was about 2∼3 times higher than the average MSA concentration of this cruise. This enhancement is supposed to be due to a large amount of DMS supplied from high CHL-a area during an air parcel transport. Besides, nss-Ca2+ concentration between May 18 and 20 was about 3∼4 times higher than the average concentration of this cruise. Trajectory analysis and other approaches such as analysis of physical properties of aerosols in this period showed that Kosa particles were observed in the atmospheric marine boundary layer. An influence of Kosa particles on the marine production and succeeding sulfur emission should be explored.
As part of Aerosol Characterization Experiment (ACE) -Asia campaign, a comprehensive study was conducted from March to April 2001 on board NOAA R/V Ronald H. Brown over the North Pacific, the East China Sea and the Sea of Japan. More than 20 research groups participated in this research cruise for the measurements of aerosol chemical, physical, and optical properties, as well as the measurements of precursor gases, seawater, and radiant flux. Authors' research group conducted an aerosol study on the chemical speciation of organic compounds, including a series of dicarboxylic acids, fatty acids, and levoglucosan. The spatial distributions of oxygenated organic compounds over the western North Pacific clearly demonstrate that Asian outflow regulates the concentrations of organic aerosols in the marine atmosphere.
The regional scale aerosol transport model (CFORS) was used in the analysis of Asian aerosol transport during the ACE-Asia intensive observation. CFORS aerosol fields were examined with the Mie scattering Lidar observation and satellite driven aerosol index, and accurately reproduced many observed features. In these comparisons, we found that an extremely large dust event that occurred in early April was produced by several dense dust layers between the boundary layer and upper troposphere. Analyses of CFORS AOTs showed that aerosol of different kinds are almost simultaneously transported over downwind regions. Analyses of aerosol horizontal fluxes clearly showed transport trends: the main dust flow is eastward along the 40°N and the carbonaceous flow in the free atmosphere is along about 30°N from south-east Asia. Finally, the regional budgets are examined and dry deposition, gravitational settling, and wet deposition of dust accounted for 33 %, 27 %, and 9 % of total emissions, respectively. Regarding carbonaceous aerosols, the eastward outflow has the highest fraction (49 %) . Transport in the free atmosphere is an important transportation process of Asian carbonaceous aerosols.
Fogs are thought to play an important role in deposition of acidic constituents in the atmosphere and also to be closely related to the decline of forests. We applied the polymeric water absorbent of a commercial diaper to the measurement of the deposition flux of fog water, for the first time. The absorbent was molded into a disk of 13 mm in diameter and 1mm in thickness, and characteristics of the disk, such as water vapor absorptivity and water retention ability, were studied in detail. Then we exposed the disk to the artificial fog in a cloud experiment facility, a large-scale vertical shaft (a long vertical passage or space in a mine) of Kamaishi Mine in Iwate Prefecture, in which a steady fog suitable for methodological studies on fogs was formed. The disks were hung on branches of a model pine tree, and the flux was determined from the increase in weight, the surface area of the disk and the exposure time to the fog. It was found through the present new method that the deposition flux was almost independent of wind directions, being 46 ∼ 65 g/m2/h. These values fell in the range of past data for tree leaves reported in literature.